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How to Part Off on a Lathe

Guide · Updated October 28, 2026

Parting off cuts a finished part free from the bar with a narrow blade. It is the lathe job most people dread, but nearly all trouble comes from height, rigidity and feed.

Check the length

Check part length with a caliper or mic verified against gage blocks; the free Gage Block Calculator builds the stack.

Step by step

Lock it down: Lock the carriage and snug the gibs so only the cross slide moves.
Minimize stickout: Part close to the chuck and keep blade stickout just over the radius being cut.
Set height: Set the blade tip exactly on center or a hair above.
Square the blade: Square the blade to the spindle axis so the sides do not rub.
Set speed: Use about half to two-thirds of normal turning speed.
Feed steadily: Feed firmly and steadily — about 0.002–0.004 in/rev for HSS on small lathes — with plenty of oil.
Finish the cut: Ease off just before the part drops, and catch it rather than letting it fall into the chips.

Worked example

1 in steel bar, carbide parting insert at 250 SFM: RPM = 250 × 3.82 / 1 ≈ 955. RPM rises as the tool nears center on CSS machines; on a manual lathe, start around 500–600 RPM and feed 0.003 in/rev.

Chatter and dig-in

Chatter usually means too little feed or too much stickout. Rubbing work-hardens the steel. A dig-in usually means the tool is below center or the compound or gibs are loose.

Rear tool post parting

An inverted blade in a rear tool post pushes the chips down and lifts the cross slide less, which helps on light lathes.

Tips

Set height first: setting tool height.
Use turning speeds and feeds as a starting point, then slow down.
Chamfer before parting so the part comes off deburred.
Never part between centers — the part can bind and throw.

FAQ

Why does my parting tool chatter?

Usually too light a feed, too much stickout, or loose gibs.

Should a parting tool be on center?

Yes, on center or very slightly above.

What speed should I part off at?

Roughly half to two-thirds of normal turning speed.

Can I use oil when parting?

Yes, plenty of cutting oil helps on steel.

Why does the blade break near the center?

The nub grows and the tool rubs or climbs; keep feed steady and the tool on center.

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General shop information only — follow your machine and tooling manufacturer's instructions and your shop's safety rules.